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roby1984

OpenGL OpenGL camera motion in a 3D application

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Hi, I'm doing a university project that consists of a 3D visor (that is, an application that plots in a 3D environment a certain kind of objects (like lines, points, ...) and allows navigation through them by using mouse + keyboard to see how the scene is composed from different positions). I'm using wxWidgets with an OpenGL canvas and I work with C++. Following the suggestions provided in one of Nehe's tutorials I've created two quaternions, one for the pitch and one for the heading (snippets of the code are below, I can provide the full source code to anyone willing to read it). My problem is that when I perform a rotation, the keys seems to be "locked" to the old xyz-axes, I mean, if I perform a 180° rotation around myself, the "w" key goes backward in the scene instead of forward. How can I "lock" the keys to operate on the new reference system? Thanks in advance to anyone willing to help me. Roberto << header file >>
  Quaternion heading_;
  Quaternion pitch_;

  GLdouble headingDeg_;
  GLdouble pitchDeg_;

  GLPoint position_;

<< initialization in the constructor >>
  pitchDeg_ = 0.0;
  headingDeg_ = 0.0;

  position_.x_ = 0.0;
  position_.y_ = 0.0;
  position_.z_ = -15.0;

<< rotations are performed using the mouse >>
void
GLCanvas::OnMouse(wxMouseEvent& event)
{
  GLdouble delta;
  mouseX_ = event.GetX();
  mouseY_ = event.GetY();

  if(event.Dragging()) {
    if(mouseX_ < centerMouseX_) {
      delta = GLdouble(centerMouseX_ - mouseX_);
      ChangeHeading(-0.01 * delta);
    }
    if(mouseX_ > centerMouseX_) {
      delta = GLdouble(mouseX_ - centerMouseX_);
      ChangeHeading(0.01 * delta);
    }
    if(mouseY_ < centerMouseY_) {
      delta = GLdouble(centerMouseY_ - mouseY_);
      ChangePitch(-0.01 * delta);
    }
    if(mouseY_ > centerMouseY_) {
      delta = GLdouble(mouseY_ - centerMouseY_);
      ChangePitch(0.01 * delta);
    }
    Refresh(false);
  }
}

<< keyboard is used for translations/strafe >>
void
GLCanvas::OnKeyboard(wxKeyEvent& event)
{
  switch(event.GetKeyCode()) {
    case WXK_UP:
      ChangePitch(3.0);
      break;
    case WXK_DOWN:
      ChangePitch(-3.0);
      break;
    case WXK_LEFT:
      ChangeHeading(-3.0);
      break;
    case WXK_RIGHT:
      ChangeHeading(3.0);
      break;
    case (int)'w':
      position_.z_ += 0.3;
      break;
    case (int)'s':
      position_.z_ -= 0.3;
      break;
    case (int)'a':
      position_.x_ += 0.3;
      break;
    case (int)'d':
      position_.x_ -= 0.3;
      break;
    case (int)'z':
      position_.y_ -= 0.3;
      break;
    case (int)'x':
      position_.y_ += 0.3;
      break;
    case (int)'b':
      ChangeHeading(-180.0);
      break;
    default:
      event.Skip();
      break;
  }
  Refresh(false);
}

<< perform rotation + translation and plot two teacups >>
void
GLCanvas::Render()
{
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  /**
     Roto-translation matrix
   **/
  GLdouble rotMatrix[16] = { 1.0, 0.0, 0.0, 0.0,
			     0.0, 1.0, 0.0, 0.0,
			     0.0, 0.0, 1.0, 0.0,
			     0.0, 0.0, 0.0, 1.0 };

  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();

  RotateCamera(rotMatrix);
  glMultMatrixd(rotMatrix);

  TranslateCamera(rotMatrix);
  glMultMatrixd(rotMatrix);

  glColor3d(1.0, 0.0, 0.0);
  glutWireTeapot(3.0);

  glPushMatrix();
    glColor3d(0.0, 1.0, 0.0);
    glTranslated(4.0, 4.0, 4.0);
    glutWireTeapot(3.0);
  glPopMatrix();

  glFlush();
}

<< camera rotation obtained through quaternions >>
void
GLCanvas::RotateCamera(GLdouble* rotMatrix)
{
  Quaternion tmp;

  pitch_.CreateFromAxisAngle(1.0, 0.0, 0.0, pitchDeg_);
  heading_.CreateFromAxisAngle(0.0, 1.0, 0.0, headingDeg_);

  tmp = pitch_ * heading_;
  tmp.CreateMatrix(rotMatrix);
}

<< camera translation -- I chose to perform it by hand >>
void
GLCanvas::TranslateCamera(GLdouble* rotMatrix)
{
  rotMatrix[12] = position_.x_;
  rotMatrix[13] = position_.y_;
  rotMatrix[14] = position_.z_;
}

<< pitch movement >>
void
GLCanvas::ChangePitch(GLdouble degrees)
{
  pitchDeg_ += degrees;

  if(pitchDeg_ > 360.0)
    pitchDeg_ -= 360.0;
  if(pitchDeg_ < -360.0)
    pitchDeg_ += 360.0;
}

<< heading movement >>
void
GLCanvas::ChangeHeading(GLdouble degrees)
{
  if((pitchDeg_ > 90.0 && pitchDeg_ < 270.0)
     || (pitchDeg_ < -90.0 && pitchDeg_ > -270))
    headingDeg_ -= degrees;
  else
    headingDeg_ += degrees;

  if(headingDeg_ > 360.0)
    headingDeg_ -= 360.0;
  if(headingDeg_ < -360.0)
    headingDeg_ += 360.0;
}

[Edited by - roby1984 on July 24, 2008 1:27:59 PM]

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This should be a pretty easy problem to solve, but could you edit your post and enclose your code in [source] tags? That'll make it much easier to read.

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I'm sorry for having skipped code tags... Might someone help me now, please?
Thanks in advance.
Roberto

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The problem is that you camera is translating in world cordinates and not in local. While I may know the problem unfortunately I don't know the solution as I am currently experiencing the same issue. I will keep returning to see if a solution is posted, and if I find one I will post it here. Sorry I can't help more than that and good luck!

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I've thought the same thing, now I'm having troubles with the remote loading of the displayed objects, but as soon as I'll fix this I'll try to find out a solution for the rotation problem (and, in that case, I will post it here). Thanks for your reply!

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I've found a tutorial written by Philipp Crocoll on CodeColony (http://www.codecolony.de/), it's the "advanced camera" example. I've studied it thoroughly, made some improvements and it worked (or, at least, now it seems to work!!).
I've put my application's source code here:
http://roby1984.netsons.org/3DVisor-0.0.3.tar.gz
(if you're interested in what my application is, just have a look at the other thread I've opened on this forum, "fglrx + OpenGL display lists - segmentation fault (long post)")
You're probably interested in GLCanvas.cc and GLCanvas.hh under the src/ directory (they lack some comments, but I've just terminated the tests of the new camera motion and I've thought you were impatient to have a solution to the problem, however my source code + the tutorial + the tutorial's source code should suffice to understand how the camera works...)
Hope this helps!
Roberto

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[update]
I've fixed a bug regarding the rotation around the Z axis and added some comments to the code... Enjoy!
Roberto

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